This protocol will attempt to (1) evaluate feedback inhibition of the HPA axis in elderly combat veterans and controls; (2) assess suprapituitary activation of the HPA axis using the metyrapone stimulation test; (3) characterize lymphocyte glucocorticoid receptor activity as a measure of the dynamics of the HPA axis; and (4) charctarize the circadian rhythm of cortisol, ACTH, NE, and MHPG using chronobiological techniques.